The invention relates to a positive connection between a pipe and a ring inserted into the pipe, in particular a positive connection between a tubular housing of a ram boring device and a stop ring inserted into the housing.
Positive connections between a pipe and a ring can be achieved, for example, by screwing or inserting a ring which is resiliently compressible radially into an annular groove of the pipe or, according to German Patent Specification 4,231,400, by inserting annular segments into an annular groove.
In the case of ram boring devices which possess a switch control from forward operation to reverse operation, the switch control is effected in that the percussion piston is braked at a forward reversing point, essentially without transmitting its kinetic energy to the device housing, with the aid of the operating air, and the rear dead center position is displaced backward. In the rear dead center position, provision is made for the percussion piston to discharge its kinetic energy, for example, against a rearward stop ring. In a ram boring device described in German Published Application 196 17 603, this stop ring is screwed into the rear end of the housing of the ram boring device and serves as a support for a control pipe projecting into a percussion piston chamber of the percussion piston and a control sleeve arranged concentrically thereto.
The screwing in and out of the stop ring, which is necessary in order to exchange wearing parts in the ram boring device, is time-consuming, since the thread is relatively long and is usually secured against unintentional loosening by an adhesive in the thread, which has to be destroyed by heating in order to break the connection.
The positive connections of the type mentioned initially between a pipe and a ring inserted into the pipe also exhibit these disadvantages. An additional factor in the case of ram boring devices is that the stop ring, in reverse operation, receives the ram impacts of the percussion piston and transmits them to the housing, for which reason it must consist of a material of adequate strength. Even so, it does happen that the stop ring breaks in the region of the thread.
The object of the invention is to provide a positive connection between a pipe and a ring inserted into the pipe, in particular between the tubular housing of a ram boring device and a stop ring inserted into the housing, which can be assembled and dismantled simply and is tolerant of high impact stresses.
Starting from this statement of the problem, the invention proposes a positive connection between the pipe and the ring inserted into the pipe, wherein the inside wall of the pipe possesses a groove in the form of a section of a surface of a sphere and the ring possesses a complementary outer surface, the inside wall of the pipe possessing at least one axial groove permitting insertion of the stop ring into the pipe or the outer surface of the ring possessing at least one flattened portion permitting insertion into the pipe, or the ring being divided axially into at least two preferably unequal segments.
In one embodiment, two flattened portions may be provided on the ring, lying diametrically opposite one another, and may be rounded to a radius corresponding to the radius of the inner surface of the pipe.
Assembly is possible in that the ring is pushed into the pipe parallel to the axis of the pipe when the flattened portion or portions, extending in the direction of the axis of the pipe, rest on the inner surface of the pipe, until the ring is located in the region of the groove which is, for example, convex in cross section. If the ring is now twisted through 90xc2x0, so that its plane stands perpendicularly to the axis of the pipe, the ring with its likewise convex outer surface fits positively into the convex groove of the pipe. Axial forces and the ram impacts of the percussion piston during a reverse movement of the device are transmitted by the convex outer surface of the ring, with the exception of the flattened portions, to the surface of the convex groove, and this takes place all the more effectively the more closely the ring with its convex outer surface is fitted into the convex groove.
If the ring has no flattened portions, but if an axial groove or two axial grooves lying diametrically opposite one another are arranged in the inside wall of the pipe, assembly takes place in exactly the same manner.
If, for example, the pipe is warmed or the ring cooled before the insertion of the ring, so that they can be brought together with sufficient assembly play, the cooling of the pipe or the warming of the ring in the assembled position can result in a clamping fit, so that the ring can no longer change its position. Similarly, a groove for a conventional snap ring can be arranged on one or both sides of the ring, so that tilting of the ring is no longer possible after the insertion of the snap ring.
The ring may also be axially prestressed with the aid of an elastic block or by means of screws, so that in forward operation, despite a slight axial play, it is fixedly secured between the housing groove and the ring.
The positive connection according to the invention is particularly suitable for arranging a stop ring in the tubular housing of a ram boring device. This stop ring receives the impacts of the percussion piston during reverse operation and passes them onto the housing.